Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. As technology has progressed, the demand for smaller semiconductor devices with improved performance has increased. As feature densities in the semiconductor devices increase, the widths of the conductive lines, and the spacing between the conductive lines of back-end of line (BEOL) interconnect structures in the semiconductor devices also need to be scaled down.
Several approaches have been implemented in order to meet these demands. As the widths of the conductive lines reduce, the spacing between two successive layers with conductive lines also reduces. The reduced spacing may therefore increase resistance-capacitance (RC) time delay. To reduce the RC time delay, low dielectric constant (low-k) materials are being used as insulating materials, and copper is replacing aluminum for interconnect structures. Advantages of using copper for semiconductor device interconnects include abilities to operate faster and manufacture thinner conductive lines because copper has lower resistivity and increased electromigration resistance compared to aluminum. Combining copper interconnects with low-k dielectric materials increases interconnect speed by reducing the RC time delay, for example.
Copper interconnects are often formed using damascene processes rather than by direct etching. Damascene processes are typically either single or dual damascene, which include forming openings by patterning and etching inter-metal dielectric (IMD) layers and filling the openings with copper. However, there are some challenges in the copper damascene structure, such as stress migration (SM) issues between the copper interconnects. The stress migration issues may cause device reliability failure.